Generally, in the field of organic synthetic chemistry, a sulfonamide compound is synthesized by means of a condensation reaction of a corresponding sulfonyl chloride compound and a corresponding amine, and the sulfonyl chloride compound is synthesized by chlorinating a sulfonic acid group. A similar process is used for forming a sulfonamide for a colorant of a dye or a pigment. A sulfonyl chloride is prepared for a colorant by using chlorosulfonic acid, phosphorus pentachloride or phosphorus trichloride when chlorinating a sulfonic acid group. However, known chlorination techniques are industrially not satisfactory because they are accompanied by a problem of sub-reactions that can arise at the time of chlorinating sulfonic acid groups, which sub-reactions are, for example, that a sulfonic acid group is introduced anew into the skeleton of the colorant or that the skeleton of the colorant is decomposed.
A method of using thionyl chloride for chlorinating a sulfonic acid group is disclosed in an attempt of avoiding such sub-reactions (see Japanese Patent Application Laid-Open No. H07-242651). However, the colorant that is the reaction substrate used in the disclosed chlorination technique is a xanthene type colorant and no technique that is applicable to a triphenylmethane type colorant has been reported so far.
Meanwhile, the advancement of science and technology has given rise to changes in the life style and colorants are currently being used in various industrial fields not only to dye or color various materials such as fiber, plastic and leather but also for the purpose of recording and displaying information. Particularly, as personal computers have rapidly become popular in recent years, there is a rapidly expanding demand for color liquid crystal displays. Color filters are indispensable for displaying color images on liquid crystal displays and are critical parts to their performances. Additionally, in line with the current dissemination of broadband systems, development of color filters that can realize enhanced spectral characteristics and a high contrast ratio has become an urgent issue for displaying high definition images.
Known methods for manufacturing color filters include the dyeing method, the printing method, the ink-jet method and the photoresist method. However, the photoresist method has been in the main stream in recent years because it can control the spectral characteristics of color filters in a reproducible manner and allows fine patterning operations because of the high resolution it provides.
Pigments are generally being used as coloring agents with the photoresist method. However, pigments have a certain size and hence accompany a depolarization effect. It has been known that the contrast ratio of color display of liquid crystal displays is reduced when pigments are used for coloring agents. Additionally, it is difficult to achieve a high transmission of backlight in a system using pigments to pose limits for improving the lightness of color filters. Furthermore, because pigments are insoluble in organic solvents or polymers, colored resist compositions are obtained in a dispersed state. However, it is difficult to stabilize the dispersion.
On the other hand, dyes are generally soluble in organic solvents or polymers and hence stable in colored resist compositions without giving rise to aggregation. Therefore, color filters prepared by using dyes as coloring agents do not accompany any depolarization effect and can achieve a high transmission of backlight because the dyes are dispersed on a molecular level. Color filters prepared by using dyes have been reported since they show excellent spectral characteristics and are adapted to display images with an enhanced display contrast.
A method of using C. I. Acid Blue 104, which is a triphenylmethane type colorant, as a colorant for blue color filters (see Japanese Patent Application Laid-Open No. 2003-5362) and a method of using C. I. Acid Red 6, which is a monoazo type colorant, as a colorant for red color filters (see Japanese Patent Application Laid-Open No. 2003-5361) have been disclosed. Of theses methods, the former method of using a triphenylmethane type colorant is particularly advantageous because of the high molar absorption coefficient (ε) of the colorant and the vivid color tone and excellent spectral characteristics.
Furthermore, a method of using an anthraquinone type colorant as a colorant for blue color filters (Japanese Patent Application Laid-Open No. 2001-108815) and a method of using a naphthoquinone type colorant also as a colorant for blue color filters (Japanese Patent Application Laid-Open No. 2002-338839) have been disclosed.